I. Field
The present disclosure relates generally to wireless communications and more specifically to transmitting reference signals to improve hearability thereof.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), etc.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more access points (e.g., base stations, femtocells, picocells, relay nodes, and/or the like) via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from access points to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to access points. Further, communications between mobile devices and access points may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or access points with other access points) in peer-to-peer wireless network configurations.
Access points in wireless networks can transmit cell-specific reference signals (CRS) to facilitate identifying cells of the access points; in addition, the CRSs can be utilized to determine a location of one or more mobile devices or other devices using trilateration or similar location mechanisms. For example, techniques such as observed time difference of arrival (OTDOA) in universal mobile telecommunication system (UMTS) are used to compute a possible location of a device based at least in part on measuring a time difference of multiple signals received and/or location of the transmitter of each signal. Similar techniques in other technologies include enhanced observed time difference (E-OTD) in global system for mobile communications (GSM) enhanced data rates for GSM evolution (EDGE) radio access network (GERAN), advanced forward link trilateration (AFLT) in CDMA2000, etc.
In addition, technologies such as idle period down link (IPDL) and time-aligned IDPL (TA-IPDL) in UMTS, as well as highly detectable pilot (HDP) in CDMA2000, improve hearability of the CRSs by blanking (e.g., temporarily ceasing) transmissions over certain periods of time. In IPDL, one or more access points can blank transmission in a different period of time (e.g., a slot of subframe defined as an IPDL period) allowing a device to measure CRSs of access points that are normally strongly interfered by other access points during the periods where the interfering access points blank transmissions. Performance gains, however, are limited by blanking only one interfering access point in a given IPDL period. In TA-IPDL, the access points can define a similar common time period, referred to as a TA-IPDL period. During this period, some access points will blank transmissions while others transmit an access-point specific pilot allowing devices to measure this pilot free from substantial interference. The HDP concept in CDMA2000 uses the same principle as TA-IPDL. TA-IPDL, however, is not always applicable in asynchronous networks. Moreover, in IPDL and TA-IPDL, legacy mobiles that are not aware of the periods of time for blanking and/or transmitting common pilots, can cause data errors. For example, lack of pilots or pilot modification can result in channel estimation errors and/or hybrid automatic repeat/request (HARQ) buffers corruption due to the assumption that the pilots exist.